418 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



greatest efficiency, relating power input to excavation production, can 

 probably be attained with 2-cubic-yard buckets. Designed so that six 

 such buckets would always be in contact with the bottom, a ladder 

 dredge, it is claimed, would provide an efficient means for digging at 

 135-foot depths. 



Large dipper dredges, although impracticable for such deep work, 

 can be used for slightly shallower digging, particularly in hard ma- 

 terial, and the Bucyrus-Erie Co. holds a third design contract for such 

 a machine capable of working at a 90-foot depth. With a 20-yard 

 bucket for hard digging and a 30-yard size for softer material, the use 

 of four 250-horsepower motors on the main hoist of such a dipper 

 dredge, supplemented by a 165-ton counterweight, would provide 

 speedy operation and large production. For all the proposed dredges 

 there seems to be a preference for self-contained Diesel-electric power 

 units rather than relying on an outside energy source. The cost of any 

 one of the dredges, it is rumored, might run as high as $5,000,000. 



Another important consideration in the deep- dredging plan relates 

 to drilling and blasting procedures under such great depths of water. 

 Such work has never been done before, and powder-company estimates 

 of the amount of explosives required are quite variable — from 2 to 4 

 pounds per cubic yard of rock removed as compared to conventional 

 charges of l^ to 1 pound. Tests now under way in the Atlantic 

 approach to the third locks cut, however, prove that the Gatun sand- 

 stone, a relatively soft rock, can be broken to sizes for handling by any 

 of the contemplated dredges with only slightly over 1 pound. Similar 

 deep-drilling and blasting tests are planned in the hard basalt rock 

 that prevails on the Pacific side. 



Powder costs could, however, be doubled or tripled without any im- 

 portant consequence. Getting the holes down is what will run into big 

 money. The actual drilling at great depths adds no new difficulties, 

 according to the present tests, so that the crux of the drilling question 

 will be speed and how to attain it ; whether by exceptionally long drill 

 steel or by the development of techniques to coimect more conventional 

 lengths rapidly; whether by a few supersize drill boats or by large 

 numbers of smaller ones; and whether by rotary or percussion-type 

 drills. 



TIDE CONTROL 



Any sea-level canal, no matter how or where built, will require a 

 number of auxiliary structures and special construction operations. 

 Thus, structures that will exclude unwanted currents, as from tides 

 or from entering rivers, are of prime importance; while the necessary 

 canal alignment to assure ease of navigation and the required side 

 slopes to obviate slides will affect dry as well as wet excavation 

 practices. 



